Voluntary written informed consent will be obtained from the parent/guardians for participation of children including their vaccination and sampling of blood and stool for various assays (Appendices). Healthy children (1 - 5 years) and adults (18-45 years) both males and females living in the Mirpur field site, who are not currently enrolled in any other research study, whether conducted by ICDDR,B or other organization, will be screened and enrolled subject to meeting the eligibility criteria. Similar procedures will be followed for part of the Dukoral study that will be conducted in Shahrasti.